Duchesneau began his career at the Montreal Urban Community Police Service in 1968. He first appeared in the public eye in 1981, when as a young sergeant-detective, he arrested his own boss for stealing drugs from the evidence locker. From 1994 to 1998, he commanded the SPCUM and simultaneously served as treasurer of the International Centre for the Prevention of Crime, vice-president of the Canadian Association of Chiefs of Police, and president of the Quebec Association of Police Directors. After retiring from his police career in 1998, he campaigned to become the Mayor of Montreal with his party Nouveau Montréal, finishing second with 26% of the vote, behind incumbent Pierre Bourque but ahead of former Mayor Jean Doré. After losing the race and failing to secure a seat as city councillor, he retreated to the private sector. In 2002, he was appointed as the first president and chief executive officer of the Canadian Air Transport Security Authority, a then newly formed Canadian Crown Corporation in response to the events of 9/11. Duchesneau retired from CATSA in 2008 to become an adjunct professor in the faculty of social science at the University of Ontario Institute of Technology. Duchesneau entered the public eye again in early 2010, when the Quebec provincial government, shaken by corruption scandals, appointed him to lead an anti-collusion unit within the Transport Ministry, which would eventually be integrated within the larger Permanent Anti-Corruption Unit. In the fall of 2011, Duchesneau leaked to the media a devastating 88-page report documenting cases of corruption and describing an entangled web of links between construction companies, organized crime, Transport Quebec and political donations. He was fired a month later. Testifying on June 14, 2012 in the inquiry of the Charbonneau commission, whose mission is to probe the corruption in Quebec’s construction industry, regarding his motive to leak the report, Duchesneau said he feared his findings would be shelved, arguing the then transport minister, Sam Hamad, showed ‘complete disinterest’ in the report. On August 5, 2012, five days after the start of the provincial election campaign, Duchesneau confirmed that he was going to run as a star candidate for the upstart Coalition Avenir Québec, led by François Legault. His candidacy was said to be a 'game-changer' in the election. He subsequently won a seat as an MNA in the riding of Saint-Jérôme.
